Heat exchanger



G. ILUNE HEAT EXCHANGER April 2, 1957 Filed July 22} 1952 5 Sheets-Sheet l April 2, 1957 a. lLUNE HEAT EXCHANGE-R 5 Sheets-Sheet 2 INQEN TQR GEORGES IL (/NE 5 9? ATTORNEY Filed July 22, 1952 G. ILUNE HEAT EXCHANGER April 2, 1957 Filed July 22; 1952 5 Sheets-Sheet 5 walls. of drawn tubes which,while -having satisfactory strength,

United States Patent HEAT EXCHANGER ,Georgcs llune, Paris, France Application July-.22, 1952, Serial No. 360,147

Claimspriority, applicationtFrance September 13, 1951 *6 @laims. (GI. 1'22'-1 82) This invention relatesto atheatsgenerator and exchanger apparatus.

The problem of heat exchange between a source .generating heat by c0mbustionof;a:fuel (such as coal,

oil, ;gas, or-the like) sand a fluid,,generally water, to be heated thereby, raises diflicultieswhich'have not been fullyasolved up to date,towing towthe fact that all of the factors involved in the "processt have not been takeninto account.

ln'the present state of the art, the'hi'gh-temperature tgases originating from the combustionsource cannot with tvery'iew exceptionspractically :be;placed indirect contact withthe heated fluid and as a result, in known heat generator an'd exchanger devices, said fgases need tobe separatedfrom the heated fluidbyt a partitionhav'ing high thermal conductivity which necessarily should be as thin as possible. Because however the pressure of th'e heated fluid, usually water, whose boiling temperature r is comparatively low, increases rapidly, the I containers'in which such fluid is stored and which are in contact with the hot combustion: gases must i be provided with i very :strong At present such containers are made in the form nevertheless need to "be provided with a comparatively very great-length, because their developedsarea issmall andbecause the outer surface of a tube doesinot receive an-equal number of heat units throughout its 'entire area, and therefore inherently pre'vents full use being made of the entire peripheral area of the-tube.

In another connection, "it one compares the transmission of heat by radiationwith transmission' by convection, it is seen that, especially when one considers colored ilames, the radiation factor is considerably higher tha'n the convection factor at temperatures above S 0O degrees C. 'It would, consequently,be logical to i'ncrease that and expensive to construct a combustion chamber ha'vi'ng walls comprised of tubes, which'constructionwould have to -beused if it were desired to make full useof radiation heat transmission in cases where the fluid to be heated is supplied under pressure. Fo'rthis reasbn conventional heat exchangers "generally have the major part of their heating surface exposed to convective heat transmission.

As a result of the foregoing considerations, heating surfaces of considerable area have to --be provided in order to obtain outputs of any substantial amountgr'esulting in necessarily voluminous exchanger =unit's, which it would be expensive and difficult to construct except by using brickworkythe use of brickwork in tur-n is iinconsistent with an ideallyr-gasetight COIlStTLICfiOIlr'Of the eon:- bustion chambers, :fiues and conduits, :so "that "leakage and ingress of col ir annot :be entirely i limina Since therefore the construction of a pressurized com- 2,787,256 "Patented Apr. 2, 1957 2 bustion chamber is not practically attainable, the combustion of the fuel is in fact performed in a suction area,

which entails as sequels a low oxygen content-in*thc combustion air, production of channels through the combustion mass through which the combustion gases flow,

pooragitation of the combustion mass, ingress of cool air, and a correspondinglylow convection heat transmission factor.

'in'view of all the above factors-which may be sum- -marized asincluding: long tubes, thick container Walls,

Another object of the invention is to provide an imtproved heatgenerator and exchanger unit in which the metallic structure issimplified, 'is comparatively light in weight-and correspondingly inexpensive to construct'an'd easy to install.

A'further object is to provide such a unit which in operation will display a very high eiiiciency ratio'unat- -tainab1e with the use of conventional heat exchangers 'and/ or generators.

A further object-is to provide such a unit which is easier to maintain, operate and control than similar units of conventional design "A more specific object is to provide in a heat generator 'and exchanger apparatus a plurality of heat-exchange zones of decreasing average temperature, the arrangement being such that the hottest zone (or zones) has a large surface area exposed to direct radiation from the sourceof heat, whereas the cooler zone (or zones) possesses large surface areas exposed to heat exchange by convection between the adjacent zones.

-A-1elated object is 'to provide in a heat ge'neratorand exchanger apparatus a plurality of concentric comparatively thin fluid circulation areas so arranged about a centrally located heat generating chamber that the average temperatures in said zones successively diminish-outwards from said chamber, the innermost and hottest of said zones being exposed todirect radiation and conduction from a source of heat in said chamber, and the successively cooler outer Zones being in convective heat exchange relationship with one another, whereby a de creasing temperature gradient is established about said chamber outwards therefrom adapted to promote thermal insulation without the use of lagging or the like and making for high thermal efficiency.

A further object is to provide such an apparatus or unit which comprises a lightweight sheet metal structure easy-to fabricate, instali and maintain, and wherein provision is made for free relative expansion between the "structural components subjected to different temperature ranges, relative to one another and with respect to a general supporting name.

A further object is to provide a heat generator and exchanger unit having .a perfectly gas-tight 'cc-i'nbustioh :axially :of a :sealed enclosure and which :is accordingly adapted to be subjected to an increased pressure, fluid to be heated being made to circulate around said enclosure in the form of a sheet of comparatively small depth or thickness.

The above and further objects, features and advantages .of the invention will appear as the description proceeds,

in which exemplary embodiments of the invention will be described by way of illustration but not of limitation, with reference to the accompanying mainly diagrammatic drawings wherein:

Fig. 1 is an elevational view, partly in section, illustrating the principle of the design of a heat generator and exchanger unit according to the invention;

Fig. 2 is an elevational view, partly in section along line II II of Fig. 3, of one practical form of embodiment of the unit;

I Fig. 3 is a plan view corresponding to Fig. 2; Fig. 4 is a side view corresponding to Fig. 2;

Fig. 5 is a sectional view taken on line V-V of Fig. 4. First referring to Fig. l, a heat generator and exchanger vunit is shown essentially comprising an inner body defined by two spaced walls 1 and 2 delineating therebetween a space 3, said body internally defining an enclosure 4 hereinafter termed the combustion chamber.

Provided at the top of the combustion chamber and coaxially with the vertical center line thereof is a source of heat shown as comprising a gas burner supplied with gaseous fuel through a line 5, primary and secondary air being delivered to the burner through the pipe lines 6 and 7 respectively. It will be understood that any other suitable source of heat may be substituted for the burner shown. Preferably, the burner nozzle is made to open into a carburizing nozzle or funnel t; provided with side .ports 9 whereby the shape of the flame produced by the fluid and to the upper limit of flow velocity selected therefor in each individual instance of use. The space 3 at its top communicates through conduits 10 with an outlet conduit 11 through which the heated fluid is discharged.

The fluid before flowing into the space 3 flows through a space defined by the walls 12 and 131 of a recuperator body or structure surrounding the double-walled inner enclosure. Surrounding in turn the recuperator structure is a sheet casing element 1 and two cylinders 15 and 16 defining between them a space 17.

The fluid to be heated is supplied through a conduit 18 and delivered by a pump 19 and a conduit 20 into the space 21 defined by the two walls 12 and 13 of the recuperator structure. From this space the heated fluid is conducted over lines 22, collector 23 and lines 24 and 25 into the space 3.

The combustion gases issue from the chamber 4 and are adapted, prior to being evacuated through the flues 26, to travel through the space 2.7 defined between the inner body and the recuperator body, then through the space 28 defined between the recuperator body and the sheet metal casing 14.

The combustion air for the burner is supplied through the grated ports 29 and then flows between cylinders 16 and 15, then between cylinder 15 and casing 14.

Owing to the above arrangement of the flow circuits, at maximum amount of the heat generated by combustion of the fuel is effectively recovered, inasmuch as the com- .bustiou gases before being discharged from the apparatus are used to preheat the fluid flowing in the recuperator structure and also to preheat the combustion air supplied .to the burner.

' p The various structures comprising the apparatus are freely suspended at their top ends and are secured at their bottom in sealing relation with a base S provided with an inspection and cleaning door 30 and having associated with it the various lines delivering the fluid.

The primary air is discharged into the line 6 by a blower 3i and the secondary air is discharged into the line 7 by a blower 32; in this way, and owing to the sealed condition of the combustion chamber 4, this chamber may be pressurized, that is a pressure in excess of the atmospheric pressure may be maintained therein.

The heat generator and exchanger described above in its basic principle may practically be constructed in the manner now to be described with reference to Figs. 2 to 5. As shown there is provided a combustion chamber 51 having two spaced walls 51a and 51b defining between them a free space 52. The combustion chamber may assume the approximate shape of a sphere, and may consist of a surface of revolution coaxial with the main vertical axis of symmetry of the apparatus. At the bottom of the combustion chamber 51 is formed a tapered section 53 provided with an opening 53a through which the interior of the chamber 51 communicates with a bottom bowl or basin 54 serving as a sealing member. The top of the combustion chamber is sealed by a top cover 55 serving at the same time as a distributor casing for the secondary air. Freely suspended within the combustion chamber 51 through an annular or other suitable support 55a is a radiating cone or funnel 56 consisting of two or more sections so as to be freely expansible. Formed in the annulus or other support of the radiating cone 56 are a plurality of ports 57 which may be provided with tubes if desired for the passage of secondary air, the top cover 55 being for-med with openings or ports 58 .so as to enable viewing the flame from outside the combustion chamber 51.

The fluid to be heated enters the space 52 surrounding the combustion chamber 51 from the basin 54 through one or more tubes 60 forming an expansible loop. To provide for the discharge of the heated fluid from the space 52, the latter is provided at its top with tubes 61 connected group-Wise with tubular collectors 62. The area of the top of the space 52 connecting with the tubes 61, is so shaped that the fluid to be heated is prevented from dwelling there in a motionless condition, thereby preventing local overheating. From the collectors 62 the fluid is conveyed over the lines 63 to the external circulating pumps 63a or to an external flow circuit if the circulating pumps are arranged upstream rather than downstream from the heat exchanger. It is to be noted that in the arrangement illustrated, according to which the pumps 6311 are placed at the outlet of the heated fluid, the fluid cannot be delivered under pressure. As regards the external circulating pumps, these are preferably secured on frames 64. on the base 65 of the apparatus (Fig. 4).

The source of heat of the apparatus comprises a burner fed with any suitable fuel such as oil or gas or pulverized coal, arranged in a central opening 66 in the combustion air distributing casing or top cover 55. The preheated primary air is forced into the air casing 55 and is there mixed with the fuel and heats the latter as it enters the combustion chamber 51. The combustion of the fuel is thus accomplished within a hermetically sealed enclosure and under a pressure substantially equal to the pressure loss sustained by the combustion gases through the apparatus; the pressure may be controlled by adjusting the damper 68 arranged in the flue 67 by means of an operating wheel 69 (Fig. 2 and Fig. 5

The preheated secondary air is discharged by the fan 70 into the air casing 55 and enters the latter through a tangentially disposed conduit 71. This air then enters the combustion chamber 51, a major part of the air flowing through the funnel 56 and a smaller part passing through the ports 57. The air entering through the ports 57 is directed around the outer cover or frame of the funnel 56 and is thus cooled somewhat, and is then conveyed along the inner wall of the combustion chamber 51 to facilitate the combustion of any fuel particles which may have escaped from the combustion zone centrally of the chamber. It should be noted further that this air causes the formation of a blanket of cool gas along said inner wall Slawithout, however, absorbing the radiation from the combustion zone (owing to the absence of CO2 and H20).

The combustion gases then flow between the outer wall 55122 that surround the space 52 and the inner wall 72a of the recuperator body 72. In order to increase the heat exchange area between the combustion gases and the walls 51!: and 72d with which the gases are in contact, the outer wall 51b of, the space 52 is provided with V-shaped fins (such as '73, Fig. 5) adapted to increase its effective surface area; the inner Wall 72a of the body of recuperator 72. is also provided with similar fins (such Pig. 5) increasing the surface area thereof. The space 75 defined between the two walls 72a and 72b of body 72 is predetermined in relation to the flow velocity which is desired to impart to the combustion gases.

The space 52 surrounding the combustion chamber the space 75 in the recuperator body 72 are provided with guiding vanes or bafiies respectively designated 76 and "7'7. These vanes are preferably made of semi-round iron bars and are secured to the inner face of the outer wall 72!) of the recuperator body 72, so as to leave a passage allowing the heated fluid to flow out between said vanes 76 and 7'? and the inner faces of the two inner walls file and 72a, respectively defining the spaces 52 and Owing to this arrangement the fluid being heated, discharged pulse-Wise by a feed pump (not shown) is caused to travel, on the one hand, over a spiral path rising through the two spaces 52 and 72 and, on the other hand, at high velocity over a by-pass path between the aforesaid walls and the guide vanes 76 and 77. The vanes 76 and 7'7 are so adjusted that these tWo paths will form an angle of about 60 between them, resulting in a turbulent condition of the fluid which will prevent local overheating thereof.

The fluid to be heated in the recuperator body 72 is supplied from the outside by the lines 78 which extend through the base 65 of the unit and penetrate into the space 75 of the recuperator body after having been passed through the bottom bowl 54. The lines 78 are formed with expansion loops.

The fluid issuing from recuperator body 72. is conveyed by the lines 79 to the collectors 80 which direct it towards the line 81 leading into the bowl 54 through the tubes 82; the fluid then passes from the bowl 54 into the space 52 of the combustion chamber 51 over the lines 60 as previously mentioned.

As a result of the arrangement described in the foregoing, the fluid is methodically circulated from the coolest zone (the space 75 of the recuperator body) towards the hottest zone (the space 52 surrounding the combustion chamber 51) through the intermediate temperature zone (bowl 54).

East as the inner wall 72a is provided with the fins 74, the outer wall 72b of the recuperator structure 72 is likewise provided with V-shaped fins 33. The fins 83 may be provided in a number twice that of the fins 74 in order to balance the heat transmission on the opposite sides of the recuperator body, and to compensate for the fact that the inner side is situated in a zone wherein the temperature is higher than that in which the outer side is located.

All the fins such as 74 and 83 are formed with spaced slots (e. g. about 10 millimeters wide and spaced e. g. 100 mm. between one another) serving, on the one hand, to increase the convection transmission factor and on the other hand to reduce the strains on the two-walled body or structure. The slots are preferably disposed in staggered relation for more evenly distributing said strains.

The combustion gases, after having travelled upwards down towards the base 65, through the gap 85 defined between the outer wall 72b of the recuperator body 72 and the inner face or Wall 8612 of the main enclosure or casing 86 of the unit. The combustion gases are thus made to give up some of their heat content to this main casing before they flow through an opening 86a (Fig. 2 formed in the top plate 109 of the base 65 and enter the flue 67 controlled by the gate or damper 68 (Fig. 5) whence they are discharged to the stack.

A number of vanes 87 which at the same time serve as supports for the centrally located components of the apparatus, are arranged so as to regularize the flow of combustion gases towards the stack through the circular fine 67. These supporting vanes act to transmit the weight of the central section of the apparatus, through four legs 88 (shown as channel sections) to the two transverse frame members 89 (likewise shown as channel sections) welded to the frame of the base 65, which frame is comprised by section iron elements reinforced with gusset plates.

The arrangement just described facilitates hoisting and transporting the apparatus. For this purpose suitable recesses, hooks, or the like are provided on the upper circular belt girder of the base constituted by the section iron 90 for receiving the chains or cables or slings or a hoist. It will further be noted that the unit comprises at its base a frame 91 made of heavy section elements .whereby it may simply be arranged upon a suitable surface as of a concrete slab without requiring any foundations. This is made possible owing to the very low weight of the entire unit, even in the case of intermediate outputs of the order of 2,000,000 calories per hour.

In order to prevent the escape of any combustion gases from the chamber 51 towards the interior of base 65, the inputs 78 which extend through the bowl 54 are provided with an asbestos stuffing and with means for ad justing the compactness thereof. Similarly a further circular asbestos packing 92 is provided for preventing any by-pass of the hot gases between the combustion chamber 51 and the flue 6'7 .and obliges the gases to flow upwards through the annular space 84. An explosion trap-door 93 fitted with a casing 94 for the protection of operators and with an inspection conduit 95 connecting it with the lower bowl 54 is provided as a safeguard against the possibility of excessive pressure build-up within the combustion chamber 51. A gas-tight door 96 provides access into the casing 94.

The combustion air necessary for the operation of the burner is drawn in from outside through a protective grating 97. This air then passes between the router casing 98 and an intermediate partition 99, flows around the lower end of said partition and rises through the gap between the inner face of the partition 99 and the outer face of the wall 35b of the main enclosure 85 which is provided with V-shaped fins similar to those previously mentioned. These fins do not only serve to increase the heat-exchange area between the wall 86b of the main enclosure 85 and the combustion air, but also strengthen the support of the intermediate partition 99.

The preheated air issuing from the space between partition 99 and wall 865 enters through ports 100' into the circular collector or manifold 100 provided at the top of the apparatus, whence it is drawn by means of the suction fan 70 through the conduit 101 and thence through line 71 provided with adjustinl gate or damper 102 into the air distributor casing 55. The casing is provided with a safety door 103 (Fig. 3) for safeguarding against excess combustion air pressure and through which access may be had to the funnel 56 for inspection and maintenance.

in order to provide for a maximum recovery of the heat tending to be carried away out of the apparatus, the heat insulation of which is provided by the air drawn greases infrom outside, a plurality of apertures 104 are provided spaced around the unit and through which air preheated by the bowl 54 and the flue 67 may be drawn from within the base 65 and mixed with the outer air drawn in by the suction fan 70. As a result, the air supplied from outside is already preheated by the air from the base 65.

A set of openings 105 (Fig. 3) are arranged on the same circumference as the tubes 79 for the outlet or the heated fluid from the recuperator body 72 and serve for inspecting and cleaning (as by an air-blast, brushing or washing) the annular passages 84 and 35 through which the combustion gases circulate. Likewise, side doors 106 (Fig, are provided on the flue 67 and large doors 107 (Figs. 4 and 5) on the base 65 for inspecting and cleaning said flue and the interior of the base respectively. I w H {The connection of the flue 67 with the stack is provided bya strong angle girder 108. The stack should be capable of providing for the low draft which is only necessary when the burner is operating in idling condition, in order to prevent clogging of the combustion chamber 51 and of the gas conduits during periods when the combustion air fan is operating with a very low rate of delivery as well as on starting the burner.

The openings 58 in the top cover 55 are provided with transparent protecting means and the handwh eel 69 for operating the damper 68 is provided. in an elevated position to enable the top plate of the base 65 to be placed at floor level, so that the flue 67 may be directly connected with the masonry smokeflue extending under the ground slab of the apparatus.

As will appear from the foregoing disclosure, the doublewalled bodies or structures comprising the space 52 arid therecuperator 72 are freely suspended from the top 55 of the unit and are supportedby the main casing 36. Owing to the fact that the casing 86 expands upwards while said structures expand in a downward direction, it follows that the relative positions of these components remain practically unaltered in the operation of the unit. As concerns the external casing 98. also suspended from the top, this casing does not expand materially because it is surrounded with cool air. The casing 98 will therefore, during expansion of the main casing 86, slide within the main base member provided by a strong annular-shaped angle girder formed with an inner bevel on its upper end to prevent damage to the apparent portion of the casing 9% during the latters displacements. The requisite seal between the combustion chamber 51 and the flue 67, during changes in the relative positions between the expanding bodies and the main casing, is provided by the annular packing 92 around the bowl 54.

It will be understood that while a single construction of an improved heat genera-tor and exchanger unit according to the invention has been illustrated described in detail, this single embodiment is by no means restrictive of the scope of the invention, since many modifications may be made in the structural details thereof. Thus, for instance, in cases where the high-temperature intermediate fluid supplied by the heat exchanger is used for generating steam, an evaporator being for this purpose provided, a steam superheat means may be interposed between the body of the space 52 and that of recuperate-r 72. For this purpose, the tapered bottom portion of the recuperator 72 may be omitted and this part may be made cylindrical to enable housing the superheat tubes. Likewise, the combustion air for the burner may be delivered by a blower arranged outside the unit, in which case the intake grating may be omitted. It should be noted furthermore that. instead of suspending the tunnel within the combustion chamber, it might be placed on its support so as to be situated outside the combus- ,tion chamber. ivioreover, the combustion may be caused angle, depending on the position of the unit. Where upward combustion is used, the bowl of the combustion chamber as well as the gas discharge conduits would be provided adjacent the top of the unit. It will be noted moreover that more than two double-walled bodies or structures may be provided, and, for instance, two recuperator structures instead of a single one may be used.

I claim:

1. Heat generator and exchanger apparatus, which comprises a; first structure having two spaced walls together at the lower ends thereof and defining internally of the inner one of said walls a sealed combustion cham ber in the form of a body of revolution, a second structure having two spaced walls sealed together at the lower ends thereof and surrounding the outer wall of the first structure in spaced relationship therewith, heat generating means within said chamber, a frame, means freely suspending the tops of both structures from said frame, a base member, said walls of the first structure at the sealed lower ends thereof extending into said base member for free expansion relative thereto and said walls of the second structure at the sealed lower ends thereof engaging the top of said member in sealing relationship therewith and for free expansion relative thereto, whereby said base member defines a sealed bottom for said chamber while providing communication from said chamber to the space between the two structures through which hot gases from the chamber are adapted to flow into and through said space, and means for circulating fluid to be heated from a fluid inlet first into and through the space between the walls of the second structure then into and through the space between the walls of the first structure to a fluid outlet, wherein said structures are generally cylindrical over a major vertical extent thereof with inwardly tapering lower sections, and said base member comprises an upwardly flared dish-like member having its upper periphery engaged by the lower end of said tapered section of said second structure in sealing relation therewith for free movement of said lower structure end with respect to said member.

2. Apparatus as claimed in claim 1, wherein said fluid circulating means comprises a first conduit means extending from the fluid inlet into said base member at a point adjacent the base of said member and up through said member into the lower sealed end of the space defined between the walls of said second structure, and a second conduit means extending from the uppermost sealed end of said space back into said base member at a point adjacent the base thereof and up through said member into the lower sealed end of the space defined between the walls of the first structure.

3. Heat generator and exchanger apparatus which comprises, a pair of coaxial structures defining a combustion chamber inwardly of the innermost one of said structures, each structure comprising a pair of spaced concentric walls interconnected at the lower ends thereof and defining therebetween respectively an inner and an outer fluid space, a gas space defined between said structures communicating with said chamber at one end thereof, means sealing both said chamber and said gas space at said communicating ends thereof, an air casing sealing the other end of said chamber, fuel burner means adjacent said other chamber end coaxially therewith supplied With primary air from said air casing, a nozzle structure supported across said chamber adjacent to and in alignment with said burner means for directing and distributing the flame therefrom throughout said chamber and having a cone-shaped outer periphery, ports peripherally of said nozzle structure for directing secondary air from said air casing along the outer periphery of said nozzle structure and the inner periphery of said first structure, means for circulating fluid through said outer then through said inner fluid space to an outlet, means for circulating combustion gases from said chamber through said gas space and thence to a stack, and means for supplying combustion air to said air casing and thence to said chamber for maintaining a superatmospheric pressure within said chamber.

4. Apparatus according to claim 3, wherein there is a further and outermost structure having two spaced concentric walls coaxially surrounding said outer structure in spaced relationship with the outer wall thereof, said outermost structure defining an air-circulating and -preheating space between the walls thereof and a further combustion gas circulating space between the outer Wall of said outer structure and the inner wall of said outermost structure, means for circulating said combustion gases from said chamber first through said firstmentioned gas space then through said further gas space and thence to a stack, and means for circulating air from an air inlet through said air space to said air casing.

5. Apparatus according to claim 4, wherein there is a concentric partition wall intermediate the walls of said outermost structure and defining an outer and an inner air-circulating and -preheating space therein, for circulating the air from said air inlet first through said outer then through said inner air space in counterflow relationship and thence to said air casing.

6. Heat generator and exchanger apparatus which comprises, a first structure having two spaced walls defining a first fluid space therebetween and defining inwardly of the inner one of said walls a sealed combustion chamber in the form of a body of revolution, :1 second structure having two spaced walls defining a second fluid space therebetween and surrounding the outer wall of said first structure in spaced relationship therewith, fuel burner means arranged coaxially with said combustion chamber, nozzle means defining a heat radiating funnel supported near one end of said chamber in alignment with said burner for evenly distributing the flame therefrom into the chamber, means for circulating fluid to be heated from an inlet through said second fluid space then through said first fluid space then to a fluid outlet, and means for circulating combustion gases from said chamber through the space between said structures, whereby the hightemperature fluid circulating through said first fluid space is heated primarily by radiation and the lower-temperature fluid circulating through said second fluid space is heated primarily by convection, wherein said nozzle means comprises more than one arcuat'e section defining a freely expansible annular structure freely supported adjacent the top of said chamber.

References Cited in the file of this patent UNITED STATES PATENTS 484,350 Waterman Oct. 11, 1892 1,704,038 Ellyson Mar. 5, 1929 1,814,605 Mayr July 14, 1931 1,841,230 Vuia et al Jan. 12, 1932 1,970,747 Hamn et al. Aug. 21, 1934 2,174,663 Keller Oct. 3, 1939 2,223,856 Price Dec. 3, 1940 2,301,683 Dalton Nov. 10, 1942 2,545,903 Swendson Aug. 30, 1945 2,552,044 Huet May 8, 1951 2,593,032 Johnson Apr. 15, 1952 2,621,635 Joostcn Dec. 16, 1952 FOREIGN PATENTS 807,903 France Jan. 25, 1937 419,626 Italy Apr. 1, 1947 

